As is known in the art, the use of relays has been proven to be effective in transmitting data from the source to the destination where shadowing or large distance is a major concern.
Recently distributed channel coding has been proposed to further increase the benefit of relaying by allowing a relay node to transmit partial codeword along with the direct transmission from the base station. See for example B Zhao and M. Valenti. Distributed turbo coded diversity for the relay channel. Electronic letters, 39:786; M. R. Souryal and B. R. Vojcic. Cooperative turbo coding with time-varying Rayleigh fading channels. Proc. IEEE ICC, pages 356-360, June 2004; and B. Zhao and M. Valenti. Practical relay networks: A generalization of Hybrid-ARQ, IEEE Journal on Selected Areas in Communications, 23(1):7-18, Jan. 2005.
The main idea of distributed channel coding is that devices in the network are able to cooperate in order to provide reliable communication. The destination receives better signal quality and achieves additional diversity by combining the information it receives from both source and relay. However conventional distributed channel coding schemes either require complex signaling for feedback between a relay node and the source or allow a relay node to forward erroneous information resulting in a performance loss.
More particularly FIG. 1 shows a typical relay scenario wherein data that has to be sent from the source (S) to the destination (D) is relayed via Relay Station (RS) where a gain is obtained since the relay station (RS) has a better link quality than the direct link between the source (S) and the destination (D) and FIG. 2 shows a typical distributed channel coding scenario, wherein an additional direct link is also used between the source (S) and destination (D) is also used. Within distributed channel coding scenario, the source (S) sends data to both relay station (RS) and destination (D) as the first transmission. After receiving data the RS decodes and forwards data to the destination (D) as the second transmission. The relay station (RS) can decode received data from the source (S) correctly or incorrectly.
As is also known in the art, relay systems with feedback, such as shown in FIG. 3 have been suggested, see for example, Y. Cao and B. Vojcic. Cooperative Coding using Serial Concatenated Convolutional Codes. IEEE Communications Society/WCNC 2005. In the relay with the feedback scheme as shown in FIG. 3, the source (S) sends data to both relay station (RS) and destination (D) within the first transmission. After receiving the data from the source (S), the relay station (RS) attempt to decode the data from the source (S) and sends acknowledgment back to the source (S) about the success. In cases where the source (S) is also the base station (BS), the source (S) is also responsible for allocating resources for transmission. Otherwise, the base station (BS), which is a central entity that controls the transmissions between the source and the destination, is responsible for allocating resources for transmissions and notifying both the Source (S) and the Destination (D) of such allocations. At this point there are two possible scenarios: First, if the relay station (RS) decodes the first transmission from the source (S) and the source (S) receives an acknowledgement (ACK) from the relay station (RS), the base station (BS) will allocate resources for the relay station (RS) to forward information to the destination (D); and Second, if the relay station (RS) is unable to decode the data from the source (S) sent in the first transmission correctly, the relay station (RS) will send negative acknowledgment (NACK) and inform the source (S) that retransmission is needed. Therefore, the source (S) retransmits information related to the first transmission to both the relay station (RS) and destination (D). That is, the retransmitted information contains the same amount of information as the message in the first transmission but the representation used in the retransmission may be different from that used in the original transmission. Depending on the type of retransmission scheme, the source (S) may retransmit the same packet (HARQ-Chase Combining) or it may retransmit additional redundancy compared with first transmission from the source (S) to the destination (D) (HARQ-Incremental Redundancy). In order to accommodate feedback between the relay station (RS) and the source (S), the base station (BS) needs to allocate additional bandwidth for transmission of ACK messages and the relay station (RS) needs to process the data unit very quickly in order to send ACK in time.